You may need (or want) to run Windows, or other operating systems, alongside your Apple Mac's Mac OS X, and Parallels Desktop is the best-known of several programs on the market for that purpose.

(Full native Windows support, of course, is also available via Apple's Boot Camp, but it requires you to reboot out of OS X and into Windows.)

A new-to-the-Mac player now brings a formidable challenger to the arena, however. VMware, an expert in x86 virtualisation — that is, the ability to run one or more x86 operating systems as "guests" under a "host" x86 operating system—has released Fusion 1.0, its first OS X offering. Like Parallels, Fusion allows you to run many versions of Windows and other operating systems from within OS X. And unlike Boot Camp, you don't have to log out and restart in order to use it.

VMware Fusion supports more than 60 operating systems: Windows coverage extends from version 3.1 to betas of Windows Server 2008. If Linux is your cup of tea, you'll find support for Red Hat, Ubuntu, SUSE, Mandrake, and more. You can also install Novell Netware, Solaris 9 or 10, FreeBSD, and MS-DOS systems. Even 64-bit releases of Windows and some families of Linux, such as Red Hat and SUSE Enterprise Linux, are supported.

As a Windows machine

Fusion runs Windows quite well - we tested it with Windows XP Pro and Windows 2000. Fusion also supports Vista, although some features (such as Unity and driver support) aren't fully functional with that OS. Given that Vista is still relatively new, this isn't surprising.

One of the key factors that differentiates Fusion from Parallels is Fusion's ability to use two CPU cores within a virtual machine; Parallels can't, and this makes a big difference in the performance of CPU-intensive tasks. It also seems to pay off by giving you a generally more responsive Windows experience.

Fusion has an Easy Install mode for Windows Vista, XP, and 2000. We tested this with a fresh XP Pro installation, and it worked perfectly — installing Windows in a virtual machine via Easy Install is actually easier than installing Windows on an actual Windows PC.

After Windows boots for the first time, you need to install VMware Tools on top of it using the Virtual Machine: Install VMware Tools menu item. This package improves graphics performance, adds support for shared folders and drag-and-drop, automatically grabs and releases the mouse pointer when in the virtual machine, and much more. VMware Tools can (and should) be installed on top of both Windows and Linux virtual machines.

Other paths to Windows

You may already have Windows installed on your Mac via either Parallels or Boot Camp, and Fusion will let you use either (or both) of those installations as Fusion virtual machines. Setting up your Boot Camp partition as a Fusion virtual machine is quite simple, and it worked perfectly in our tests.

We weren't asked to reactivate Windows again, although some users have reported this problem. To avoid this and other issues, make sure you follow the instructions in VMware's help documents (Help: VMware Fusion Help, then search for Boot Camp) exactly as they are written.

The process of converting a Parallels virtual machine is more complicated. You'll need to read the instructions in the Converting a Parallels Virtual Machine to Run in VMware Fusion PDF file, which you can download from the VMware site. We worked through the conversion process (including adding multiple CPU support), and while it took about an hour to process our 10GB Parallels virtual machine on an Apple Mac Pro, it did work as described.

The process isn't overly complicated, but there are a number of steps to follow. When it's done, you'll have your Parallels Windows installation up and running in Fusion, with the exact same programs and files as you had in Parallels.

Adobe Reader, Firefox, Safari, and Trillian all ran as expected—compatibility in Fusion with typical Windows applications such as these is excellent. The programs load quickly, are stable, and work as well as they do in a native Windows environment.

Video playback in Windows Media Player, even using high-definition demo clips from Microsoft, was smooth. We had a bit of trouble with audio lag and skipping in a few of the QuickTime video clips, but they were generally still easy to watch.

We were also able to use the DVD burner on the Mac Pro to add files to a CD-RW disc, and the iSight camera works, so long as you install the iSight drivers from Apple's Boot Camp Windows drivers disc.

Fusion also supports some 3D games, though the support is limited to older DirectX 8.1 games. Fusion's release notes list only 11 supported games, all much older than the 40 or so listed on Parallels' site. (Fusion 1.1, now in beta, will add support for DirectX 9.0, which should expand the list of supported games.) We were able to find and run demos for a few of the games on the list, and they worked reasonably well - a steering wheel worked in the driving games, for instance, although the force feedback did not. If you really want to play games on your Windows Mac, though, Apple's Boot Camp provides the best performance.

Fusion includes excellent USB 2.0 support, so you shouldn't have any trouble with most third-party devices — not even products such as GPS receivers and Windows Mobile phones. We weren't able to get a Wacom tablet working in the Windows XP virtual machine; a search of the VMware forums revealed that this is a known issue.

An Intel-based Mac (to run 64-bit operating systems, an Intel Mac with a Core 2 Duo or Xeon processor is required) 512MB of RAM (1GB or more recommended) 275MB free disk space for VMware Fusion 1GB free disk space for each virtual machine (10 GB or more recommended) Mac OS X version 10.4.9 or later

Ease of Use:

Features:

Value for Money:

Overall:

Fusion 1.0 is a viable competitor to Parallels, and for consumers, that's a good thing. Already, the release of Fusion has inspired an incremental upgrade in Parallels so that its Coherence feature more closely matches what you get with Unity—and there's the upcoming Fusion 1.1 that will add better 3D graphics support, improvements in Unity mode, support for the Eject key, and a host of other improvements. We found Fusion easy, fast, stable (we had no hard lockups during my testing), and very well thought out. Its game support doesn't match that of Parallels, but if you're serious about gaming in Windows, you're not going to be using either of these programs anyway. Although it's a very close call between these two excellent virtualization programs, we prefer Fusion for its low impact on other OS X applications, support for multiple virtual CPUs, and huge library of virtual appliances.

The two best options for running Windows (or any other OS) on your Mac are Parallels Desktop or VMware Fusion. Here we compare Parallels and VMware to answer the question: what's the best way to run Windows on a Mac?